TBI idle

[Ontheboulder]

Just rebuilt my TBI. fired right up but after a couple minutes the idle would drop then come back up? no codes to see maybe throttle position sensor? runs good other than the idle dropping the rising back to normal. Any ideas??thanks

 

[dusterdude]

You might need to re-set the iac motor

 

[Rusty Nail]

Low coolant level.

 

[Ontheboulder]

Low coolant level.

coolant is full,coolant sensor is new

 

[Rusty Nail]

Didja reset the IAC motor?

 

[Ontheboulder]

Didja reset the IAC motor?

not sure how to do that! any help?

 

[gmbellew]

not sure how to do that! any help?

you should be able to cycle the key to on for 10 sec, off for 5 sec, and then start it. you can also jumper AB terminals of the OBD port with. paperclip and turn key to on for 30 sec. then pull jumper and start it. either one should get the job done.

 

[Ontheboulder]

you should be able to cycle the key to on for 10 sec, off for 5 sec, and then start it. you can also jumper AB terminals of the OBD port with. paperclip and turn key to on for 30 sec. then pull jumper and start it. either one should get the job done.

THANK YOU!

 

[Rusty Nail]

@dusterdude

 

[TFerguson]

not sure how to do that! any help?

In case you still need some guidance on this, here are the steps I always follow to reset the IAC:

1. Ensure timing is set correctly, get to operating temp, & turn off engine
2. Put a jumper pin (paper clip) on upper right (last two on top row) ports on OBD connector
3. Turn key to ON position
4. Wait about 30 secs (allows IAC valve to set itself to fully closed)
5. Unplug IAC connector from TBI (big connector on pass rear of TBI)
6. Ensure the idle screw is accessible on the drivers front of TBI (will need to *carefully* drill out cover if still in place)
7. Have a Torx 20 screwdriver handy for the idle screw
8. Connect timing light or some other device that will display RPM
9. Start engine (might have to give it some gas to idle since IAC not connected)
10. Set the idle screw to desired RPM (typically 650-700)
11. Turn off engine
12. Disconnect the negative battery cable and connect neg cable to pos batt terminal (supposedly "resets" ECM cache, per some guy on YouTube)
13. Plug IAC connector back in
14. Unplug jumper wire (paper clip) from OBD port
15. After 5+ minutes, reconnect the battery to neg cable (after removing conn to pos term)
16. Turn key to On and wait 10 secs
17. Start engine & confirm idle speed is correct before & after test driving

 

[TFerguson]

In case you still need some guidance on this, here are the steps I always follow to reset the IAC:

1. Ensure timing is set correctly, get to operating temp, & turn off engine
2. Put a jumper pin (paper clip) on upper right (last two on top row) ports on OBD connector
3. Turn key to ON position
4. Wait about 30 secs (allows IAC valve to set itself to fully closed)
5. Unplug IAC connector from TBI (big connector on pass rear of TBI)
6. Ensure the idle screw is accessible on the drivers front of TBI (will need to *carefully* drill out cover if still in place)
7. Have a Torx 20 screwdriver handy for the idle screw
8. Connect timing light or some other device that will display RPM
9. Start engine (might have to give it some gas to idle since IAC not connected)
10. Set the idle screw to desired RPM (typically 650-700)
11. Turn off engine
12. Disconnect the negative battery cable and connect neg cable to pos batt terminal (supposedly "resets" ECM cache, per some guy on YouTube)
13. Plug IAC connector back in
14. Unplug jumper wire (paper clip) from OBD port
15. After 5+ minutes, reconnect the battery to neg cable (after removing conn to pos term)
16. Turn key to On and wait 10 secs
17. Start engine & confirm idle speed is correct before & after test driving

I should add that you only need to mess with the idle screw if it does not already idle in the 650-700 range with the IAC unplugged.

 

[gmbellew]

i thought the min air idle (if there is a reason to even mess with it at all on TBI) is set 100rpm BELOW target idle on a fully warmed up engine. in the drivability manual, the idle target is 525rpm in Drive I believe. idle in Park is usually a little higher, like 50-100rpm higher when fully warmed up. but either way, setting min air adjustment to idle at 650-700 with IAC closed may result in a high idle that the computer cannot compensate for.